1. Field of the Invention
The present invention relates generally to cognitive radio networks and, more particularly, to a method for defense against primary user emulation attacks in cognitive radio networks using advanced encryption.
2. Description of the Related Art
Along with the ever-increasing demand in high-speed wireless communications, spectrum scarcity has become a serious challenge to the emerging wireless technologies. In licensed networks, the primary users operate in their allocated licensed bands. It is observed that the licensed bands are generally underutilized and their occupation fluctuates temporally and geographically in the range of 15%-85%. Cognitive radio (CR) networks provide a promising solution to the spectrum scarcity and underutilization problems.
CR networks are based on dynamic spectrum access (DSA), where the unlicensed users (also known as the secondary users) are allowed to share the spectrum with the primary users under the condition that the secondary users do not interfere with the primary user's traffic. The CR networks identify the unused bands (white spaces) through “spectrum sensing”, then utilize the idle bands for data transmissions. The spectrum sensing function is continuously performed. If a secondary user detected a primary user signal in the band that it operates in, then it must evacuate the band and operate in another white space.
The CR networks have become vulnerable to malicious attacks that could disrupt their operation. A well-known malicious attack is the primary user emulation attack (PUEA). In a PUEA, the malicious users mimic the primary user signal over the idle frequency band(s) such that the authorized secondary users cannot use the corresponding white space(s). This leads to low spectrum utilization and inefficient cognitive network operation.
PUEA have attracted considerable research attention. An analytical model for the probability of a successful PUEA based on the energy detection has been proposed, where the received signal power is modeled as a log-normally distributed random variable. In this method, a lower bound on the probability of a successful PUEA was obtained using Markov inequality. Several methods have been proposed to detect and defend against a PUEA. A transmitter verification scheme (localization-based defense) was proposed to detect a PUEA. A similar approach based on the received signal strength (RSS) was proposed to defend against a PUEA. A Wald's sequential probability ratio test is used to detect a PUEA based on the received signal power.
In most existing methods, the detection of a PUEA is mainly based on the power level and/or direction of arrival (DOA) of the received signal. The basic idea is that: given the locations of the primary TV stations, the secondary user can distinguish the actual primary user's signal from the malicious user's signal by comparing the power level and DOA of the received signal with that of the authorized primary user's signal.
A major limitation with such state-of-the-art methods described above is that they would fail when a malicious user is at a location where it has the same DOA and comparable received power level as that of the actual primary transmitter. Therefore, there is a need in the art for a new method for defense against primary user emulation attacks in cognitive radio networks.